Conventionally, there has been known a substrate processing apparatus for performing a plasma process such as plasma etching on, e.g., a semiconductor substrate wherein a substrate mounting table for mounting the substrate thereon is provided with a fluid supply mechanism for supplying a cooling gas such as a helium gas to a rear surface side of the substrate. Further, it is also known that a thermally sprayed ceramic layer such as an Al2O3 layer is formed on a substrate mounting surface of the substrate mounting table as an insulating layer which forms an electrostatic chuck (see, for example, Japanese Patent Laid-open Application No. 2004-47653).
For the manufacture of the aforementioned substrate mounting table, a manufacturing method can be considered wherein the method involves the steps of, for example, separately preparing a first plate shaped member provided with a number of gas supply openings and a second plate shaped member provided at its surface with grooves to be used as a gas supply channel through which a gas is introduced into the gas supply openings; integrating the two plate shaped members as a single body by welding them through a soldering process, for example; and then forming a thermally sprayed ceramic layer on a mounting surface by thermally spraying ceramic thereto.
In the above-described manufacturing method, the thermally sprayed ceramic may enter the gas supply openings during the ceramic spraying process. To avoid this, the ceramic spraying process is performed while ejecting air or the like from the gas supply openings, thus preventing the thermally sprayed ceramic from entering the gas supply openings. However, the entrance of the ceramic into the inside of the gas supply openings cannot be completely prevented by the ejection of the air or the like. Therefore, it is required to perform a cleaning process to wash off the ceramic that has entered the inside of the gas supply openings and adhered to, e.g., the bottom portions thereof.
According to thorough investigation, however, the present inventors have founded that the thermally sprayed ceramic firmly stuck to, e.g., the bottom portions of the gas supply openings may not be removed completely through the cleaning process, and some may remain as spray residue. If this spray residue is peeled off while a final product is in use, it would contaminate a semiconductor wafer or the inside of a processing chamber, or clog up the gas supply openings, resulting in a pressure reduction of a cooling gas and a failure in temperature control.